1. Field of the Invention
The present invention pertains to apparatus for measuring and indicating harmonic distortions in conductors, such as power lines. More particularly, the present invention pertains to a portable, simple-to-use, and highly versatile instrument for quickly measuring and indicating a range of individual harmonic distortions in conductors.
2. Description of the Relevant Art
There are known devices for detecting and/or displaying harmonic distortion in conductors. Such known devices are, for example, disclosed in U.S. Pat. Nos. 2,782,366, 3,916,296 and 3,927,281.
U.S. Pat. No. 2,782,366 discloses "oscillographic apparatus for analyzing the performance of Amplifiers, Modulators, Detectors and the like." The disclosed apparatus comprises a circuit including a test oscillator, a group of potentiometers, amplifiers tuned to first, second and any other desired harmonic, a battery, and a group of oscilloscopes for providing output displays. This known apparatus has many disadvantages. For example, it is very bulky and difficult to use, especially in remote locations. Also, this apparatus can only be used in testing individual parts which have been disconnected/isolated from their normal use, and harmonic distortion in voltage signals.
U.S. Pat. No. 3,916,296 discloses a high sensitivity/high resolution distortion analyzer including a parallel-T circuit bridge that is tuned by adjusting two variable elements, typically a resistor in one branch of the circuit and a capacitor in a second branch of the circuit. The tuning is achieved by separate feed-back circuits that utilize a +45.degree. or a -45.degree. phase-shifted signal derived from an input voltage signal. This apparatus is substantially easier to use than that disclosed in U.S. Pat. No. 2,782,366, but still has several problems and disadvantages associated therewith. For example, the apparatus is still quite inconvenient to use (especially in remote locations) because the operator is required to turn off the power to an electrical component before connecting the analyzer thereto (resulting in expensive down time), and because the operator is required to adjust the variable elements. Also, the disclosed analyzer, like that disclosed in U.S. Pat. No. 2,782,366, is limited to analyzing the harmonic distortions of a voltage signal, and does not include any means for selectively choosing various signal harmonics to be measured.
U.S. Pat. No. 3,927,281 discloses an instrument for measuring harmonic distortion in telephone transmission lines. The instrument measures the harmonic distortion introduced during telephone line transmission, and can distinguish between the harmonic distortion introduced at the send terminal and that introduced in the receiver terminal. The disclosed instrument comprises a frequency phase lock circuit which generates "disturbance-free, in-phase and quadrature voltage signals of a received test tone, the disturbance-free generated tones being different from the transmitted test tone as a result of possible frequency shift along the transmission channel and phase shifts in the terminal equipment at both ends". As disclosed, the instrument is connected to an oscilloscope for providing an output display. This instrument has associated therewith substantially the same problems and disadvantages as discussed above with regard to the analyzer disclosed in U.S. Pat. No. 3,916,296.
Conventional distortion analyzers, including those discussed above, have many problems and disadvantages associated therewith, and have as a whole failed to fulfill a need in the art for a portable, simple-to-use and highly versatile instrument which can be used for quickly and easily locating and measuring problem-causing harmonic distortion in substantially any conductor while the conductor is in normal operation.
Additionally, the present inventors have previously proposed, in U.S. Pat. No. 4,818,947 (the '947 patent hereinafter) and 4,902,960 (the '960 patent hereinafter), apparatus for measuring harmonic distortion in a conductor. The '947 patent discloses a portable instrument for locating and measuring harmonics in a conductor based on a current input signal from an easily manipulatable current transformer which has been secured about the conductor. The apparatus includes a selector switch for permitting an operator to manually select which harmonic of the input signal is to be measured, and an auto-gain circuit for permitting harmonics to be read while a load drawn through the conductor is changing. The '960 patent discloses an optional improvement to the apparatus of the '947 patent, whereby the apparatus can receive a voltage input signal rather than a current input signal, and will measure voltage harmonics thereof. The option consists of a voltage input circuit which can selectively be coupled between a conductor and the apparatus of the '947 patent for providing an appropriate voltage input signal thereto, and a selector switch incorporated into the apparatus of the '947 patent which permits the operator to manually adjust the apparatus for either a current input signal or a voltage input signal.
Although the apparatus of the '947 and '960 patents is very advantageous over the previously known apparatus for detecting and/or displaying harmonic distortion in conductors, the apparatus of the '947 and '960 patents remains to be improved relative to convenience in use, accuracy of measurements, extent/amount of information output, etc.